1. Technical Field
This disclosure relates generally to the field of optics, and in particular but not exclusively, relates to near-to-eye optical systems.
2. Background Art
A head mountable display (“HMD”) is a display device configured to be worn on or about a user's head. HMDs usually incorporate some sort of near-to-eye optical system to display an image within a few centimeters of the user's eye. Single eye displays are referred to as monocular HMDs while dual eye displays are referred to as binocular HMDs. Some HMDs display only a computer generated image (“CGI”), while other types of HMDs are capable of superimposing CGI over a real-world view. The former type of HMD is often referred to as virtual reality while latter type of HMD is often referred to as augmented reality because the viewer's image of the world is augmented with an overlaying CGI, also referred to as a heads-up display (“HUD”).
HMDs have numerous practical and leisure applications. Aerospace applications permit a pilot to see vital flight control information without taking their eye off the flight path. Public safety applications include tactical displays of maps and thermal imaging. Other application fields include video games, transportation, and telecommunications. There is certain to be new found practical and leisure applications as the technology evolves.
Near eye displays often rely on internal reflection properties of an optical transmission medium. Redirection of light from transmission from an internal reflection structure often depends upon some type of outcoupling structure such as a diffraction grating. As the quality of near eye display technologies continues to improve, the appearance and behavior of such outcoupling structures becomes increasingly important with respect to overall user experience.